Thermocouple testing system



July 28, 1953 -r 2,647,237

THERMOCOUPLE TESTING SYSTEM Filed Nov. 17, 1950 2 Sheets-Sheet 1INVENTOR gwm ATTORNEY July 28, 1953 J. A. HERBST 2,647,237

- THERMOCOUPLE TESTINQSYSTEM Filed Nov. 17, 1950 2 Shts-Sheet 2 INVENTORBY John 4. flerbst WM ORNEY Patented July 28, 1953 STATES PATENT, 4 f

2,647,237 I J I THERMOCOUPLE 'rss'rmcs srs ii f i John A. Herbst, PinesLake, N. J., assignor, by

mesne assignments, to Bogue ElectricManufacturingCo Paterson, N. J. i

Application November 17, issmsni No. 196,122

This invention relates to a system for testing create a voltage inresponse to a; sudden rise in temperature uch as may be caused by afire, an

overheated bearing, of the like. In orderto detect a sudden rise intemperature 'due'to abnormal temperatures in a selected zone suchasj'inian airplane engine compartment, machine hearing, or the like,there has been provided a warning system based on the use of one or morethermocouples located in the selected zones. Each thermocouple comprisesa hot junction and "heat insulated reference junctions, thethermocouples being series connected with an electrically operatedwarning device, whereby a rapid rise in temperature in one or more zoneswill be effective in respect to the thermocouple junctions iri'suchzones, to generate a current which operates-the warning means. It isimportant that such systems be adapted to be quickly tested at periodicintervals, in order to make sure that the system is in good workingorder. I indicate any discontinuity in the circuits interconnecting thethermocouples and the warning 'means. However, "such known testmeanswill not indicate the presence 'of a short circuited thermocouple,false grounds which may render one or more thermocouples inoperative, orreversed polarity of connections. With the highly .sensitiveipolari'zedrelays used in such systems to operate "the warningmeans in response tothe ,c'urrent'generated by the thermocouples, reversed polarity-ofconnections on a thermocouple will render the system inoperative whensuch thermocouple is subjected to a rapid rise in temperature, since thecontinuity test is inefiective toindicate ,incorrect polarity ofthermocouple connections.

In addition, an incorrectly connected thermocouple may render acorrectly connected thermocouple ineifective, since if boththermocouples are 'su-bjectedto a rapid rise in temperature, the voltagegenerated bythe incorrectly connected :thermocouple will be inopposition to that of the correctly connected thermocouple, "leaving'the resultant voltage substantially zero and ineffective to operate therelay. v

--Accordingly, an object of this invention is to provide in athermocouple system'of the type described; a test circuit adapted to beconnected .to the system for determining the presence of one ,ormoreshorted or incorrectly connected-thermocouples, or false grounds in thesystem. 1 g

Test means has been provided which can 7 GClaims. (cram-458) Anotherobject of this invention is to provide in a system of the characterdescribed,a testfcircuit including means for heating the hot andreferencejunctions of the-thermocouplesb'y passing acurrenttherethrough,the hot junctions being heated more rapidly" than the referencejunctions, thereby-generating an E. 'M; Fhproportional to thedifierenc'ein temperature, and means for indicating the cumulative: value of theindividual voltages --of the thermocouplesin accordance' with theirrespective directions in the circuit,'whereby to detect the presence ofone or more sh'o'rt circuited or incorrectly c'onnected thermocouples.-

A further object of this invention is to provide in a system of thecharacter described, ate'stcircuit' including "meansfor passing acurrent through the junctiohs of the" interconnected thermocouples, theinsulated and-non-insulated junctions thereafter cooling atdifferentrates to thereby generate individual voltages, and means for indicatingthe cumulative value of such voltages in accordance 'with' -their'respective 'directions in the circuit, whereby *tdde'tect-the presenceof one or more short 'circuited or incorrectly connected thermocouplesjStill another object of this invention is to pro vide in arapidtemperaturerise detection'system including a groupof-'thermocouplesf'aitest circuit including a second group ofthermocouples equal in number and design to th'e'thermocouples of'the'first group, but connected 'with 'reversed polarities'as compared tothe polarity convnections, of the'first' group, together with means forpassing a current through the junctions of both groups of thermocoupleswhereby to' generate E. MS F.s in each of the'thermocouples of bothgroups, "and' means' for-indicating the algebraic sum of generated M.F.s in both groups "of thermocouples, whereby-to detect one orinoreincorrectly connected or shorted thermocouples in the "first' group',the generated M. Ffisbeing created by a differential heating er coolingeffect -as between the" hot andreference' junctions of each"thermocouple; "Still a further object of thisinve'ntioni's to 'providefor use 5 witlfa system of the character described, simple'test circuitshaving a'ininimum number of components which are readilyintericonnected, which are quickly operable to "check the system andwhichare rugged," compact" and efiicient to a high degree in use; V w

Other objects of this invention will-in part be obvious and parthereinafter 'fpoin't'ed out,

- The invention accordingly consistsin the-con binations. of"-"elements' and circuit connections Figs. 4 and 5 show modiiledi tomeofi test circuits embodying the invention.

In Fig. 1, l designates a conventional thermo couple known in the art.The same comprises a pair of wires ll, l2, of dissimilar metals-and.having their outer ends: twisted and welded together asat M forming whatis as a hot junction. Theinnen end-s at. the wirestt, Mane welded; to.short metal. elements M, 15,. respectively, asat Ha,. Ha, forming". whatare. known ascoldor reference junctions. The elements H, t are formed.on the Same metals. which. may be of stainless steet. or the like andterminate in reduced threaded pontions fla, kw, which: pro:- videterminals for electrical connections;

The assembly of. wires M, 12. and metal elements k4,. I5 ismountedspaced. electrical and heat insulating members 1%; H.- The members 16;.H are fixed within the interior ofa metal cage k8 which ieformedwiflra:plurality of openings 19 at the upper end-thereof; The hot-junc tion. I3is located opposite openings '9 so as to be treely accessible to the:atmosphere. The metaleiements H PS, which are of. much eater diameterthan: wires M, be, together withjunc We, Met are disposed; withininsulating member l1.

Each of the, themnocoupiesi k0: is adapted to be locatedin-a selected.zone which may be subjected to a: rapid rise in temperature:. Such zonesmay be various portions of an: airplane engine cormpartment, baggage orcargo compantment, electrical and hydraulic accessory compartments; amachine bearing, variousiportions of-a structure subject to firehazards; or: the like;

- The thermocouples Ht areseries connected". as

shown. in Fig 2, and are further connected in series with. the coil- Mof a. sensitive, polarized relay 2 la. The armature 22 0t relay 2 t isadapted to close a circuit through a relay 2 3, inresponse toenergiza-tionofi coil. c The: relay .23, in tum is adapted. upon.energiaatioim of the coil 23a thereof through: a current source- 24, to'have: its

varmature 2322' close a: circuit-to operate an. electrical warning.device- W, which; may take: the form of abell, a signal. light,, onthelike; coil. 231 is shunted by a resistance R. toprevent The sparkingat the contact points of the relay.-

The current. for. energizing. coil. 20* is derived from one or morethermocouples Mr when such thermocouples areexposed. to'a rapidrisein'temeffect the hot andreference-junctions; substantially equally.

However,. a..- rapid. riseof temperature, due to ,a. fire, overheatedbearing or the like. cause the hotjunction; is to healup muchxmorempidlyI than the reference junctions I la, He. The lag in heating isaccentuated by heat insulating sleeves 25 on the lower portions of wiresH, II and the relative difference in the mass of elements l4, l5 andwires H, l2.

Accordingly, a rapid rise in temperature will produce a differentialheatin eifect as between the: hot" and reference junctions ottliethem-imcouple or" thermocouplesexposed to such temperature rise, andthere will be created a voltage at terminals Ma, l5a which isproportional to the rate. of rise of. the ambient temperature. The morerapid the change in temperature, the greater be the: temperaturedifferential bethe hot junction and the reference junctiimsand thehigher the output of voltage at terminals Ma, .l5a.

The current output of one or more thermocouples. is adapted to energizethe coil of the sensitive relay 2|. The operation of relay 2| isGfiEGliiiVQl/O close the circuit-between thewamin signal W and thesource of.- current: 24,. thmmgh the: relay 23,. thus operating thewarning. signal. Inorder totestthe continuity ofthecincuitsin the systemshown in. Fig. 2,. there has. been pm vided a test circuit which.includes an enclosed thermocouple 26 having; a. resistance heater 21located adjacent' the. hot. junction thereoi. .Ehe heater 2-1 isconnected. circuit with the source oi current; M through a normallyopenbutton switch-.28; Totest. the circuit, switch. is closed so as toheatthe resistance 21, thereby tarnishing heat sufiicient to causethermocouple; 26 to.- generate a current; If. the circuit connectionsare continuous and unbrokcm. the generated current will be effective tooperate.- relayit and: thereby operate relay 23 the. warning, signal.

Such. a test circuit however, will. not detect thermocouples having.improper polarity connecz. tions. A thermocouple having its terminalslbw, l5a improperly connected in theseries circuit, willnot operatethepolarized relay 21!, even though subjected to a. rapid. rise: in:temperance.- Anincorrectly connected thermocouple mam also fail tooperate. a. non-polarized; relay inasmuch assuch; a; thermocouple uponexposure to a rapid rise in. temperature may create acurrentsubstantially equal to: the current created by one or morecorrectlyconnected thermocouples also subjected to a rapid rise: temperature,.the. resultant currentbeing either zero: or insufilcicnt' 1201981 83138the non polarized relay.

Furthemncre, the test circuit shown in. 112.. 2,

will not detect a. short. circuited. thermocouple.

oitfalse grounds such. as; indicated. in dotted: lines at 29th: thefigure; In either case, a rapid rise temperature will not be detectedand: the wamng: signal W will not be operated;

Accordingly, there is provided atest emhodymg the: as shown its Fig; 3.Such circuit is: adapted to: measure the rate of rise in temperature byindicating the cumulative value oi the 3.. Ffs generated each 01. thethermocouples. and thereby indicate the-presence of. one or morethermocouples having reversed connections; one: or more shorted"themmcouples or false grounds;

Such a. circuit includes means for pawns" a. current through thejunctions of of theintercotmected thermocouples: whereby to: heat thesame, allowing the junctions to: cool and measuring. the currentscreated by the cooling efieetas between the exposed; hot jimmtima; andinsulated. reference junctions of each of the themiucmmlesi Accordingly,as shown in Fig. 3, in a circuit en-- tirely similar to that shown inFig. 2, there is provided a current source C'which is regulated by meansof a rheostat R1. The current source C is adapted to be connected incircuit with-the thermocouples ID by means of a double pole, doublethrow switch 30. The movable arms-3 I, 3 l a of switch 30 are in theform of armatures of a relay 32 which is adapted to be energized by asource of current 24a. A button switch 28a and a' timer switch TS areinterposed in the relay circuit. As shown in Fig. 3, the switch 30normally disconnects current source C from the thermocouples Ill.-

The test circuit embodying the invention further comprises'a millivoltmeter M which is adapted to'be connected in circuit with the hot andreference junctions of the interconnected thermocouples [U by means of adouble pole, double throw switch 33. The movable arms 34. 34a of switch33 are in the form of armatures of a relay 35 which is adapted to beenergized by source of current 24a upon operation of a timer switch TS1.As shown in Fig. 3, the switch 33 normally disconnects the meter M fromthe thermocouples i0.

Assuming that it is desired to test the thermocouples II) for reversedpolarity of connection, short circuit or false grounds, switch 28aisclosed." Timer switch TS is adapted to be closed for a pre; determinedtime interval during which the relay '32 is energized to operate switch30 and allow current from source C to flow through the ther-- mocouplesand thereby directly heat the hot and reference junctions of eachthermocouple.

After current ceases to flow, due to operation of the timer switch TS,the junctions will start to cool. However, with the hot junctions l3exposed and the reference junctions I' la, l2a heat insulated, therewill be a differential cooling efiect whereby an E. M. F will beproduced at the terminals Ha, |5a of each thermocouple.

Upon the lapse of a predetermined time interval after the timer switchTS disconnects the source of current C from the thermocouples and duringwhich the differential cooling efiect noted above, takes place, thetimer switch'TSi is effective to connect the meter M to thethermocouples through operation of relay 35, switch 28a being closed.The cumulative or algebraic sum of the E. M. F.s produced by the severalthermocouples 'will be indicated on the meter M.

In the event that one or more of the thermocouples l has its terminalsMa, Ia, reversely connected in the series circuit, then the E. M. F.

of such thermocouple or thermocouples will be ofiset against the E. M.F. produced by the cor rectly connected thermocouples. Thus, assumingthat each of the seven thermocouples shown in Fig.3 suppliesapproximately 1 millivolt due to the diiferential cooling effect, thenif allthe thermocouples are correctly connected, there should be areading of approximately '7 .millivolts on meter M. If one thermocoupleis reversely connected,.then its voltage will neutralize the voltage ofone correctly connected thermocouple, thus reducing the reading toapproximately 5 millivolts." The meter M progressing through negative aswell as positive readings, will indicate the number of reverselyconnected thermocouples. With all seven thermocouples reverselyconnected, there would be a reading of minus '7 millivolts.

False grounds as indicated in dotted lines at 29 in Fig. 3, will shortout a plurality of thermocouples and will be revealed by the meterreading.

Similarly, shorted thermocouples will-be indicated bythemeterreading.Alternatively, the'test circuit may be based'on voltages createddirectly by the'diiferential heat-.- ing effects as between the hot andreference junctions of each of the interconnected thermocouples, asindicated in Fig. 4. Here, the-switch 33 is adapted to beoperated byrelay-35-when switch 28a is closed, to connect the thermocouplejunctions tocurrent" source C and meter,.z;-M through the operation ofswitch 30. 1",- Thus, when the thermocouples'are' to'be tested, switch28a is closedto operate switch 33:and switch 28b is operated tOJaIIOWtimer switch TS to energize relay coil'32 for a predetermiiieditimeinterval. This will cause switch 30 to connect the current source C tothe thermocouplesa'nd to directly heat thejunctions'thereof,throughswitch 33. When timer switch TS deenergizesrelay. 32 and switch 30 is restored-to itsno'rm'ah condition, meter 'Mwill be immediately'connected to the thermocouple junctions andwillzread the cumulative value algebraicsum of thevoltagesof theindividual thermocouples created by. the differential heating effectas'betweenthe exposed hot junction I3 and the insulated referencejunctions I la, l2a and augmentedby. the increased mass of metalelements 1'4; [5. :j-Openingswitch 28a restores the system to normalcondition or for continuity test by thermocoupleZB, as previouslydescribed. The circuit shown in Fig; ,4 eliminates onatimer switch andshortens the time of the test period. Furthermore, the testedthermocouples operate. in the same manner during test as they wouldunder 'operatingfield conditions- 1 j In a further-modification of theinvention, the cumulativevalue of the voltagesvgenerated byja group ofthermocouples may be compared with that of a second group ofthermocouples used as a test standard. Thus, as shown in Fig. 5, l l ldesignates the thermocouples to be -tested, .beirig indicated as four innumber gfOIiihB purpose of illustration. A second group offourthermocouples H1, each of which :is entirelyasimilarli ndesign'tothermocouples. I0, is adapted tobe"c0nnected in. series withthermocouples ,IO, through switch 33. The meter MandcurrentsourceC areadapted to be connected to the juncjtionsof thenmocouplesv l0, Illthrough operation ofsw'itch f relay 32"and timer switch TS, as describedin ca .nection with Fig.4. Y i It'will-be noted that thermocouplesJllfarcorrectly interconnected soas to provide ayqltage in a directioncDDQsitetothat of th voltagesu'p "plied bythermocouples 10., ,Thu Q 28a isclosed, relay 35 i QPeratedfto. c 33. Switch 2812 is then closedto'permitjtimer switch TS to operate and allow current from cur rent sourceC to flow through; switch 3 3;to1th junctions of both,groups.offthermocouples. The resultant voltage will register on m eter{Mwhen timer switch TSrestores switch;30,-; to normal;; Assuming that allthe thermocouples- H1,arcefiqr rectly connected then their total.voltagegwill -b equal and opposite to the total voltage of ther'mocouples I 0' and the meter M will'give a zeroread:

mg. However; if one or mere tnerni'oeoupiesno are incorrectly connected,then a negative meter reading will indicate the number of thermocouplesincorrectly connected.

Thermocouples I0, which are always identical in number and design as thethermocouples to be tested, are conveniently mounted on a test paneltogether with meter M, the relays and switches and connected-as topolarity, in order to insure a proper offset voltage with respect to 31dinantlv looutedrimd often substantially inaccessible thermocouples ll.lt is understood that a test set of thermocouple: may also be used inthe circuit of Fig.3 wherein the voltages are createdby a differentialcooling eilect. suitable changes in connections being made to insurethat the total voltage of both acts of thermocouples is supplied to themeter M after the junctions have been heated and allowed to cool.

-1he'timer switches TS and TS; are of conventlonal type, which arepreset to allow circuits to heielosed or opened over predetermined timeThe current source C may be of the constant current time. usin therheostat. R1 or other suitthis means to keep the current supplied to thethemocouple junctions substantially constant. In this manner, the meterM may be accurately calibrated to give a known readingfor a given amountof current supplied to a given number of correctly connectedthermocouples for use as in index with respect to readings taken whenone or more thermocouples are incorrectly connected. This makes. certainthat a reading will reveal the exact number of hicorrectly connectedthermocouples.

enclosed fliermooouple 26 may be retained to test the continuity of thecircuit connections in commotion with the test circuits of the instantinvention.

It will thus be seen that there are provided test circuits for systemsof the character described, in which the several objects of theinvolition are. achieved and which are well adapted to meet theconditions of practical use. various possible. embodiments might be madeof the above described invention, and as various changes might be niadein the embodimeats set forth, it is to he understood that all matterherein set forth or shown in the accom m ving drawings, is to beinterpreted as illustrot-we and not in a limiting sense.

Having thus described my invention, I claim as new and desire to protectby Letters Patent:

1. In a temperature measuring system comprising a circuit including atleast one thermocouple having a hot Junction and heat insulatedreference junctions, test means for the circuit including a source ofcurrent of predetermined value, time controlled switch means forconnectlog said current source in said circuit for a. predetermined timeinterval, a meter and time con trolled switch means for connecting saidmeter in series with said thermocouple upon the expirathan of apredetermined time interval after the expiration of the first mentionedtime interval.

2. in a. rapid temperature rise detection system, a predetermined numberof'serics connected thermocouples, each-thermocouple comprising a hotjunction and heat insulated reference junctions, and a polarized relayin circuit with said thermocouples, a source of current of predeterminedvalue. a relay operated switch for connectlug. said source of current tosaid thermocouples, amps. a second relay operated switch for connestingsaid meter to said thermocmiples. means for closing said first mentionedswitch for a pro determined time interval whereby the junctions of saidthermocouples are heated, and means for closing said second mentionedswitch upon the expiration of a. predetermined time interval after saidfirst mentioned switch is opened whereby the total voltage produced bythe differential coolingoi the junctions of said thermocouples isindicated on said meter.

3. In a rapid temperature rise detection system comprisingapredetermined number of series connected thermocouples, eachthermocouple comprisin a hot junction and a pair of refer-- encejunctions, test means for said thermocouples comprising a source ofconstant current, a meter. switch means for connecting the junctions ofsaid thermocouples to said current source, said switch means beingadapted to connect the junctions of said thermocouples to said meter,and means operative to control the duration of the first mentionedconnection of said switch means.

4. In a. rapid temperature rise detection system comprising a group ofseries connected thermocouples having generally proper polarityconnections, each thermocouple comprising a hot junction and a pair ofreference junctions, test means for said group of thermocouplescomprising a source of current, a meter, a second group of seriesconnected thermocouples equal innumber to those of the-first group andhaving each thermocouple thereof properly connected to the adjacentthermocouple as to polarity, the thermocouples of said second groupbeing series connected to those of the first group and having thepolarity connections thereof opposition to the polarity connections ofthe first group, and switch means for successively connecting thejunctions of said groups of thermocouples to said source of current andsaid meter, whereby the cumulative voltages created by said first groupof thermocouples may be compared with the cumulative voltages created bythe second group of thermocouples by the reading on said meter.

-5. Test means as in claim 4 and further in cluding means operable tocontrol the operation of said switch means.

6. A method of testing a plurality of intercom nected thermocouples,each thermocouple comprising a hot junction and a pair of reference,iunctions, comprisin passing a current through the junctions of saidthermocouples for a predetermined time interval and measuring thealgebraic sum of the voltages produced by said thermocouples upon theexpiration of a second predetermined time interval after the expirationof the first time interval. 1

- JOHN A. HERBST.

References Cited in the file of this patent -UNITED STATES PATENTSNumber Name Date 1,206,304 Chubb Nov. 28, 1916 1,818,847 Gruss Aug. 11,1931 1,957,051 Norton May 1, 1934 2,376,920 Jones May 29, 1945 2,473,940Clark June 21, 194.9

